Fasting season length sets temporal limits for global polar bear persistence
Fasting season length sets temporal limits for global polar bear persistence
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DOI：
10.1038/s41558-020-0818-9
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发表时间：
2020-07-20
影响因子：
30.7
通讯作者：
Amstrup, Steven C.
中科院分区：
文献类型：
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作者：
Molnar, Peter K.;Bitz, Cecilia M.;Amstrup, Steven C.
北极熊（Ursus maritimus）需要海冰来捕捉海豹，随着全球变暖和海冰损失的继续，预计北极熊数量将在整个范围内下降（1，2）。估计不同的亚群何时可能开始开始下降至今还不可能，因为大多数亚群都没有将冰的可用性与人口表现联系起来的数据（2），而且对于预测的但尚未观察到的低冰极端情况（3），也无法获得先验数据。在这里，我们通过估计北极熊在幼崽招募和/或成年生存受到影响并迅速下降之前可以禁食的阈值天数，建立了未来人口影响的可能性质，时间和顺序。将这些禁食影响阈值与从地球系统模型的大型集合估计的无冰天数（4）相交，揭示了人口影响何时可能发生在北极的不同亚群中。我们的模型捕捉了1979-2016年期间观察到的人口趋势，表明在某些亚群中，招募和生存影响阈值可能已经超过。它还表明，由于温室气体排放量高，繁殖和生存急剧下降，到2100年，除少数北极高纬度亚种群外，所有北极高纬度亚种群的生存都将受到威胁。适度的减排措施虽然可以持久，但不太可能在本世纪内阻止某些亚种群灭绝。随着全球变暖，北极熊赖以捕食的海冰减少，北极熊的数量预计将下降。预测显示，海冰减少引起的禁食可能导致北极熊在环极范围内的快速招募和生存下降。
Polar bears (Ursus maritimus) require sea ice for capturing seals and are expected to decline range-wide as global warming and sea-ice loss continue(1,2). Estimating when different subpopulations will likely begin to decline has not been possible to date because data linking ice availability to demographic performance are unavailable for most subpopulations(2)and unobtainable a priori for the projected but yet-to-be-observed low ice extremes(3). Here, we establish the likely nature, timing and order of future demographic impacts by estimating the threshold numbers of days that polar bears can fast before cub recruitment and/or adult survival are impacted and decline rapidly. Intersecting these fasting impact thresholds with projected numbers of ice-free days, estimated from a large ensemble of an Earth system model(4), reveals when demographic impacts will likely occur in different subpopulations across the Arctic. Our model captures demographic trends observed during 1979-2016, showing that recruitment and survival impact thresholds may already have been exceeded in some subpopulations. It also suggests that, with high greenhouse gas emissions, steeply declining reproduction and survival will jeopardize the persistence of all but a few high-Arctic subpopulations by 2100. Moderate emissions mitigation prolongs persistence but is unlikely to prevent some subpopulation extirpations within this century.Polar bear numbers are expected to decline as the sea ice they rely on to catch their prey declines with global warming. Projections show when fasts caused by declining sea ice are likely to lead to rapid recruitment and survival declines across the polar bear circumpolar range.